Why do people keep saying that -9 squared (no parentheses) equals to -81?

The mathematical concept of squaring, often expressed as “number squared,” can sometimes lead to misconceptions or misunderstandings, particularly when dealing with negative numbers. In this 1000-word blog post, we will delve into why people might incorrectly believe that (-9) squared equals -81, the importance of mathematical notation, and the correct interpretation of negative number squares.

Why do people keep saying that -9 squared (no parentheses) equals to -81?

The misconception that (-9) squared equals -81 may arise from a misunderstanding of negative number operations. In reality, when you square a negative number, like -9, it yields a positive result, which is 81. The misconception may persist due to a lack of clarity in mathematical communication or familiarity with negative number rules.

Understanding Squaring

Squaring a number means multiplying it by itself. In mathematical notation, it is denoted as “number squared.” For example, squaring 3 results in 3 × 3, which equals 9. When working with positive numbers, this concept is straightforward and aligns with our intuitive understanding of multiplication.

The Misconception: (-9) Squared Equals -81

The misconception that (-9) squared equals -81 stems from a misunderstanding of the rules of arithmetic and the handling of negative numbers. Some individuals may interpret the squaring of a negative number as simply changing the sign of the square of the corresponding positive number.

In other words, they might mistakenly believe that if 9 squared is 81, then (-9) squared should be the opposite, which is -81. This misconception can be traced to a lack of familiarity with the correct rules for squaring negative numbers.

The Correct Interpretation: (-9) Squared Equals 81

In reality, the squaring of a negative number does not change the sign of the result. The correct interpretation of (-9) squared is as follows:

(-9)² = (-9) × (-9) = 81

So, (-9) squared equals 81, not -81. This aligns with the fundamental arithmetic rule that states when you multiply two negative numbers, the result is a positive number.

Why the Misconception Persists

Several factors contribute to the persistence of the misconception that (-9) squared equals -81:

  1. Miscommunication: In casual conversation or teaching, the notation and rules for negative numbers may not always be clearly explained, leading to misunderstandings.
  2. Lack of Mathematical Understanding: Some individuals may not have a strong foundation in mathematics or may not have encountered negative number operations frequently, which can contribute to misconceptions.
  3. Intuition and Common Sense: People often rely on their intuition and common sense when interpreting mathematical operations. While this is generally beneficial, it can lead to errors when dealing with less intuitive concepts like negative numbers.
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Clarifying Negative Number Squares

It’s crucial to clarify the correct rules for squaring negative numbers to dispel misconceptions. Here are some key points to emphasize:

  1. Squaring a negative number yields a positive result. The square of a negative number is always positive, just like the square of a positive number.
  2. (-x)² = x²: When squaring a negative number, it is equivalent to squaring its positive counterpart. For example, (-3)² = 3² = 9.
  3. The sign change occurs during multiplication, not squaring. The negative sign in (-x) is retained when squaring, but it changes to positive when multiplying two negative numbers, as in (-x) × (-x).

Practical Significance

Understanding the correct rules for squaring negative numbers is not only essential in mathematics but also has practical significance in various fields:

  1. Physics: Negative numbers often represent directions, velocities, and forces in physics. Correctly applying the rules of arithmetic is crucial for accurate calculations.
  2. Finance: Financial calculations frequently involve negative numbers, especially in accounting, investments, and loans. Accurate arithmetic is essential for financial planning.
  3. Computer Science: Algorithms and computations in computer science often deal with signed numbers, and errors in arithmetic can lead to software bugs.
  4. Engineering: Engineers use mathematical principles to design and analyze systems and structures, where negative numbers may arise in various contexts.


The misconception that (-9) squared equals -81 arises from a misunderstanding of arithmetic rules and negative number operations. It’s essential to clarify that squaring a negative number results in a positive value. By emphasizing the correct mathematical principles and notation, we can help individuals overcome this misconception and develop a stronger foundation in mathematics. Accurate mathematical understanding is not only vital for academic purposes but also for practical applications in science, finance, engineering, and various other fields where negative numbers play a significant role.

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